1. Field of the Invention
This invention relates to a focus detection apparatus and an image taking apparatus which are provided with first focus detecting means for detecting a focus shift amount on the basis of the phase difference between a pair of image signals photoelectrically converted by a focus detection sensor, and second focus detecting means for evaluating the contrast of an image signal photoelectrically converted by an image pickup sensor to thereby detect a focus shift amount.
2. Description of the Related Art
As an automatic focus detection apparatus for a camera, there is well known an automatic focus apparatus of a so-called phase difference detection manner for causing light beams from an object passed through different exit pupil areas of a photo-taking lens to be imaged on a pair of line sensors, and finding the displacement amount of the relative position of a pair of image signals obtained by photoelectrically converting the object images, to thereby detect the defocus amount of the object and effect the driving of the photo-taking lens on the basis thereof (Japanese Patent Application Laid-open No. H09-054242 (see FIG. 3)).
Also, in a digital still camera using an image pickup element, there is well known an automatic focus apparatus of a so-called contrast detection manner for detecting an in-focus position by effecting the evaluation of the contrast of an object image obtained by the image pickup element while changing the focal position of a photo-taking lens (Japanese Patent Application Laid-open No. 2001-004914 (see FIG. 1)).
Also, in an image pickup apparatus provided with both of the above-described phase difference detection manner and contrast detection manner, there is known an image pickup apparatus which stores the difference between an in-focus position detected by the phase difference detection manner and an in-focus position detected by the contrast detection manner, in advance, as a correction value, and drives a photo-taking lens from the in-focus position detected by the phase difference detection manner and the stored correction value during ordinary photographing (Japanese Patent Application Laid-open No. 2000-292684 (see FIG. 14)).
The automatic focus apparatus of the phase difference detection manner disclosed in the above-mentioned Japanese Patent Application Laid-open No. H09-054242 (see FIG. 3) can detect the defocus amount from a certain focal position to the in-focus position and therefore, the time required for in-focus detection is short. However, an object optical path obtained by the phase difference detection manner and an object optical path when photographing is actually effected differ from each other and therefore, there occurs an error between the in-focus position detected by the phase difference detection manner and the in-focus position on the image pickup surface.
Also, the automatic focus apparatus of the contrast detection manner disclosed in Japanese Patent Application Laid-open No. 2001-004914 (see FIG. 1) detects the focus by the object optical path in photographing and can therefore accurately detect the in-focus position on the image pickup surface. However, it is necessary to effect contrast evaluation calculation while changing the focal position of the photo-taking lens, and this gives rise to the problem that much time is required until the in-focus position is reached.
Also, in the image pickup apparatus disclosed in Japanese Patent Application Laid-open No. 2000-292684 (see FIG. 14), the in-focus position shift detected by the phase difference detection manner can be corrected by the correction value, but an appropriate correction value cannot be detected depending on the condition of an object when the correction value is detected, and this has led to the problem that as the result, an accurate correction value cannot be obtained. This is because when, for example, the contrast of the object is low, the error of the result of the detection by the phase difference detection manner or the result of the detection by the contrast detection manner becomes great.
Also, when use is made of a pseudo-object image for measurement of high contrast (hereinafter referred to also as the chart image), it is very difficult to accurately make the chart image and a focus detection view field coincident with each other, and a right correction value cannot be found.
Thus, the correction value changes in conformity with the measurement condition and therefore, to detect an original right correction value, it is necessary to provide a predetermined measurement condition. However, if in a factory or the like, it is easy to create a predetermined measurement condition, but it is very difficult for an ordinary user to make the predetermined measurement condition.